Dragonflies Provide Antibacterial Clues

By Stephen Luntz

A technique copied from dragonfly wings could prove the key to creating surfaces that are safe from bacteria, and could be used in implants that currently become sites of infection.

Prof Russell Crawford, Dean of Swinburne University’s Faculty of Life and Social Sciences, has been researching surfaces that resist colonisation by bacteria. “We tried putting in silver and antibacterial tea tree oils,” he says. “These stopped some sorts of bacteria, but not others.”

Crawford’s team then looked at superhydrophobic surfaces. These include cicada wings (AS, Nov 2013, pp.24–26), which they found could kill rod-like bacteria but not spherical species such as golden staph. Searching more widely they came across the wandering percher dragonfly (Diplacodes bipunctata), whose wings are lethal to all sorts of bacteria.

“Dragonflies live in a different environment to cicadas – wet, swampy areas where they would be exposed to more pathogenic bacteria,” Crawford says. “The wings are covered in sharp pillars nanometres wide that stretch the membranes of bacteria that land on them to breaking point.

“We were working with engineers here at Swinburne, and learned that people had been able to etch patterns in silicon that are similar to the dragonfly wings.”

Nature Communications has now published the discovery that silicon etched in this way, known as black silicon because the grooves absorb light, is even more effective for antibacterial purposes.

“Both surfaces were found to be highly effective against a range of bacteria, as well as endospores,” Crawford says. “They exhibited estimated average bacteria-killing rates of up to 450,000 cells per minute of exposure for every square centimetre of available surface.”

The capacity to kill spores, which have evolved to be resistant to most natural dangers to bacteria, is particularly unusual. The appropriately patterned black silicon is also the first hydrophilic surface to show antibacterial properties.

The next question is the effects of such surfaces on our own body. “Skin cells are far more resilient than bacteria, so there is unlikely to be damage if we touched a surface like this,” Crawford says. “But we still need to know if it would trigger an effect, particularly inside the body.”

Crawford suspects that the short lifespan of insects has allowed them to evolve a weapon against infection that has escaped vertebrates.